X-COM (sometimes stylized as X-Com) is a science fiction video game franchise featuring the titular fictional elite international organization tasked with countering alien invasions of Earth. The series began with the hit strategy video gameUFO: Enemy Unknown created by Mythos Games and MicroProse in 1994. The original line up by MicroProse included six published and at least two cancelled games, as well as two novels. The X-COM series, in particular its original entry, achieved a sizable cult following and has also influenced many other video games; including creation of a number of clones, spiritual successors, and unofficial remakes.

A reboot series entitled XCOM was published by 2K Games, beginning with the strategy video game XCOM: Enemy Unknown, developed by Firaxis Games and released in 2012 to critical and commercial success, with two more games following in 2013.

The premise of the franchise is that a mysterious alien invasion began in 1999 (a near future at the time of the first game's release). In response, a coalition of funding nations clandestinely create an elite paramilitary organization codenamed X-COM (an abbreviation of "ExtraterrestrialCombat Unit") as humankind's last hope. The player is charged with leading this secret force, tasked to engage and research the alien threat. Upon finishing the game successfully, X-COM manages to capture and reverse engineer enough of the invaders' technology to decisively turn it against them. The sequels took the fight against new alien invasions underwater (Terror from the Deep, set in 2040), into a futuristic megacity (Apocalypse, set in 2084), and eventually into space (Interceptor, set in 2067, which actually makes it a prequel to Apocalypse).

UFO: Enemy Unknown, featured a turn-based ground combat system, and remains the most popular and successful game in the series and has been often featured on various lists of best video games of all time.[7] The first sequel, Terror from the Deep, was quickly created by MicroProse's internal team; based on the same game engine and used largely identical gameplay mechanics. Apocalypse took several new directions with the series, introducing an optional real-time combat system and shifting the aesthetics to a retro-futuristic style. Despite being developed by Julian Gollop's British studio Mythos Games, the original creators of Enemy Unknown, it failed to repeat its smash success. The last released X-COM main game, Interceptor, constitutes a hybrid of a strategy game and a space combat flight simulator.

After Interceptor, Hasbro Interactive purchased MicroProse, acquiring its studios and the X-COM brand, and, according to GameSpy, "there was wild talk of X-COM toys, comics, and cartoon shows."[8] A budget range, turn-based tactical play-by-mail multiplayer game Em@il Games: X-COM was released in 1999. In 2001, Hasbro published X-COM: Enforcer, a poorly received third-person shooter loosely based on the events of Enemy Unknown, marking a low point in the series. The X-COM games were also released as part of four compilation releases: X-COM (Collector's Edition) (1998),[9]X-COM Collection (1999)[10] and X-COM: Complete Pack (2008),[11] as well as in 2K Huge Games Pack in 2009.

At least two more major titles were planned for this series: X-COM: Genesis (a real-time strategy and tactics game "going back to the roots but in full 3D"[12]) and X-COM: Alliance (a first-person shooter tactical game). However, both of these projects were cancelled after ex-MicroProse Hasbro Interactive studios were all shut down in 1999-2000 (although Alliance has been later abortively reactivated in 2001-2002). Years later, Terry Greer, a senior artist and head of game design at MicroProse UK, disclosed: "We'd also discussed other avenues for future [X-COM] games including time travel, retaking the solar system (with interplanetary distances playing a significant role in recruitment and resources), and resistance movement concept where you had to fight back after the world was taken and humanity was totally under the alien yoke."[12]

In April 2010, 2K Marin announced they were working on re-imagining of X-COM, relabeled as XCOM,[25] to be released for the PC, PlayStation 3 and Xbox 360. It is described as a tactical and strategic first-person shooter supposed to combine elements from the original X-COM alongside a new setting and viewpoint while keeping some main concepts from the original game series. The setting received a complete overhaul, now based in the early 1960s, with the XCOM being a U.S. federal agency. Originally planned for 2011, the game was released on August 20, 2013 as The Bureau: XCOM Declassified.

In January 2012, Firaxis Games (led by MicroProse co-founder Sid Meier) announced the development of a PC, PlayStation 3 and Xbox 360 strategy game XCOM: Enemy Unknown, a "re-imagination" of UFO: Enemy Unknown with real-time strategic view, turn-based combat and destructible tactical environments more in vein of the original X-COM game. It is also set in a more contemporary setting than the XCOM game by 2K Marin.[26]XCOM: Enemy Unknown was released on October 9, 2012 to critical acclaim, winning multiple "Game of the Year" awards. Julian Gollop hailed it as "a phoenix rising from the ashes of the X-COM disaster", saying that "it’s amazing that after 20 years, a brand that had gone so badly in the wrong direction has finally been put right."[27]

In November 2013, Firaxis released a downloadable content for the base game XCOM: Enemy Unknown titled XCOM: Enemy Within.[28] It was available on Steam (which requires Enemy Unknown to play),[29] as well as for the PlayStation 3 and Xbox 360 (both versions are standalone and do not require Enemy Unknown).

A popular add-on for XCOM Enemy Unknown is Long War, with a longer campaign duration, a more extensive tech tree, larger squads with more classes and more emphasis on the air game.[30][31]

There are two X-COM novels based on the first game in the series: Diane Duane's X-COM: UFO Defense - A Novel (1995, ISBN 0-7615-0235-1) and Vladimir Vasilyev's Enemy Unknown (1997). According to Rock, Paper, Shotgun's negative review of Duane's novel, it is hampered by a poor understanding of the game, a lack of focus, emotional resonance and tension, and an unstructured plot.[32] MicroProse's John Possidente also wrote three short stories ("Decommissioning", "Manley's Deposition" and "Moray in the Wreck") taking place between the events of the first two games in the series.

The trademark for the X-COM name was filed on May 25, 1995, by MicroProse Software. According to Julian Gollop, "They wanted us to do a deal where we would sign over any rights that we might have in return for some cash plus a high royalty on X-COM: Apocalypse. They more or less insisted on it, otherwise they were threatening to cancel the Apocalypse project, so there was a lot of bluff involved."[34] Following the acquisition and subsequent merger of MicroProse with Hasbro, the X-COM intellectual property ("IP") was also transferred to Hasbro Interactive on August 19, 1998. Due to financial difficulties, Hasbro Interactive was sold to Infogrames Entertainment, SA on January 29, 2001. As part of this transfer, the X-COM IP was legally transferred to Infogrames on December 21, 2001 (shortly thereafter, Infogrames was renamed Atari, SA). In 2005, Atari, SA transferred several IPs to Take-Two Interactive Software, Inc.[35] and X-COM was transferred with them on June 12, 2005.

The X-COM IP is currently owned by Take-Two and its subsidiaries;[36] by 2007, first rumors emerged that Irrational Games (who are owned by Take-Two) were developing a new X-COM title[37] (this game eventually became The Bureau: XCOM Declassified). In May 2007, 2K Games (a subsidiary of Take-Two) inherited the X-COM franchise and re-released Terror from the Deep on Steam. In September 2008, UFO: Enemy Unknown, Apocalypse, Interceptor and Enforcer were also re-released as downloadable titles. The first 2K Games' XCOM, which has been in works actually since 2003 (even prior to the IP acquisition),[38] was finally completed and released in 2012.

Because of the series' popularity, various developers have created spiritual successor games similar in theme and tone of the X-COM games (sometimes called "X-COM clones";[39] Gollop also himself called turn-based tactical game genre in general as "sons of Rebelstar" in a reference to one of his earlier games[40]). The level to which they borrow from the original series varies.

Isomer is an upcoming indie strategy game currently under development which was also heavily influenced by the X-COM series as well as other games such as Dwarf Fortress and Minecraft. It blends realtime strategy combat with world exploration and sandbox gameplay.[47]

Laser Squad Nemesis is a 2002 turn-based low-budget PC turn-based tactics game developed by Gollop's new company, Codo Technologies, very similar to the Battlescape ground combat system of the first X-COM game.

The Dreamland Chronicles: Freedom Ridge was a strategy game for the PC and PlayStation 2 by Julian Gollop's Mythos Games (creators of Enemy Unknown and Apocalypse), claimed to having been "essentially a remake of the first X-Com with 3D graphics".[48]The Dreamland Chronicles was canceled in 2001 and Mythos Games soon ceased to exist.

UFO: Aftermath is a 2003 single-player PC strategy and real-time tactics game which was heavily influenced by the X-COM series and used elements of the Mythos Games' canceled The Dreamland Chronicles. It was created by Czech company ALTAR Interactive and published by Tri Synergy.

UFO: Extraterrestrials, a PC strategy / turn-based tactics game that is an unofficial sequel to the X-COM games, developed by Czech developer Chaos Concept and released by Tri Synergy in 2007. The follow-up game, UFO2Extraterrestrials: Shadows over Earth was supposed to be released in Q4 of 2012; its current status is unclear.

Xenonauts is a PC strategy game by British independent studio Goldhawk Interactive, again heavily influenced by the X-COM series. It is being marketed as a Cold War-era (1979 instead of 1999) re-imagining of the original UFO: Enemy Unknown and an answer to 2K's The Bureau: XCOM Declassified which alienated some of the X-COM fanbase due to its FPS-based gameplay.[51] The game missed several release dates, but was finally released in June 2014.

A similar open source game still in pre-release phase is X-Force: Fight for Destiny.[53] Still another, Project Xenocide, was aborted in 2010.[54]

UFO Online (unrelated to UFO Online – Fight for Earth) is a tactical MMORPG that is available only in Russian.[55]

Fan-remake projects for UFO: Enemy Unknown include X-com - Last Hope (a mod of Half-Life 2 released in 2006),[56]UFO: The Two Sides (development halted in 2011 due to copyright issues),[57]UFO: Cydonia's Fall (canceled in 2012), X-COM: Origin (development still ongoing in 2012)[58] and The Rebel Squad, a defunct project by Sam Liu.[59]

OpenXcom is an open-source reimplementation of that game to fix all the bugs and enable modding.[60][61]

X-Com: Tactical is a board game reproducing the squad tactics element of the first game.[62]